读“黄土高原示意图”(图4),回答19~21题。 19.黄土高原范围的叙述,正确的是( ) A.东起黄河 B.西至太行山 C.南抵秦岭 D.北至贺兰山 20.流经黄土高原的大河是 ( ) A.长江 B.黄河 C.淮河 D.珠江 21.黄土高原水土流失严重的主要原因有 ( ) A.地形平坦 B.植树种草 C.降水均匀 D.土质疏松Four of Robert's children were at the party, including ________, Luke.
A. the oldest
B. an oldest one
C. the old
D. an old one